The present invention relates to control systems which align electrical components for precise placement via pick-and-place machines onto surfaces such as printed circuit boards, hybrid substrates containing circuitry traces, and other carriers of circuit tracings. More specifically, the present invention relates to a non-contact light-based sensor system which precisely determines angular orientation and location (x, y) of components to allow a pick and place machine to correct angular orientation of the component with respect to the pick and place machine""s coordinate system for proper placement.
The electronic device assembly industry uses pick and place machines to automatically xe2x80x9cpickxe2x80x9d components from standardized feeder mechanisms, such as tape reels, and xe2x80x9cplacexe2x80x9d such components upon appropriate carriers such as printed circuit boards. A given printed circuit board may include a large number of such components and thus the automation of component placement upon the printed circuit board is essential for cost effective manufacture. One important aspect of a given pick and place machine is the manner in which component orientation and location are detected prior to placement. Some pick and place machines transport the component to an inspection station where it is imaged by an inspection camera, or the like (i.e. off-head systems). Once imaged, the controller, or other appropriate device, calculates orientation and location information from the component image. One drawback associated with such systems is the added time required to transport the component to the imaging station; to image the component; and to transport the component from the imaging station to the placement location. Another type of pick and place machine uses an xe2x80x9con-headxe2x80x9d sensor to essentially image the component while being transported from the component feeder to the placement location. Thus, in contrast to the above example, on-head component inspection systems typically allow higher component throughput and thus lower cost manufacture.
Pick and place machines that incorporate on-head sensors are known. One such device is taught in U.S. Pat. No. 5,278,634 issued to Skunes et al., and assigned to the assignee of the present invention. U.S. Pat. No. 5,278,634 discloses an on-head component detector that uses a single light source to direct illumination at and past a component of interest, which illumination then falls upon a detector. The component fits through a fixed size window in the housing of the Skunes ""634 sensor. With the light energized, the component is rotated by a vacuum quill while the width of the shadow cast upon the detector is monitored. The minimum shadow width is registered when the sides of a rectangular component are aligned normally with respect to the source. Associated electronics, sometimes resident in the pick-and-place machine, compute the desired rotational movement of the nozzle (with knowledge of reference axes of the pick-and-place machine). This allows angular orientation of the component, as well as component position to be determined, and corrected for proper placement.
Other pick-and-place machines employ sensors with multiple light sources in the sensor, to accommodate components of varying sizes.
Although the system taught by Skunes et al. has provided a significant advance to the art of electronic component placement in pick and place machines, an efficient sensor adapted for use with components having a wide range of sizes would provide faster placement and less machine down-time to exchange sensors with different sized components.
A sensor for sensing placement information, including rotational offset, positional offset (x, y), width and length of a component to be placed by a pick and place machine is disclosed. The sensor includes a plurality of selectably energizable light sources, each of which is disposed to direct illumination at different angles of incidence upon the component. Source control electronics are provided and coupled to the plurality of light sources to successively and/or selectively provide an energization signal to each source, so that when the component is at least partially disposed in the sensing field, the component blocks illumination from at least one of the plurality of light sources to form a shadow of at least a portion of the component on the detector. Computing electronics receive the detector outputs to compute the placement information, relative to a coordinate system of the pick and place machine. The detector is adapted to provide a plurality of detector outputs while the component rotates. A detector is disposed within the sensor relative to the plurality of sources to receive at least one partial shadow of the component, and provide a plurality of detector outputs indicative of the shadow(s) imaged on the detector while the component is rotated by the pick-and-place machine.
In one embodiment of the invention, a priori knowledge of the component size is not required.